Process for recycling heterogeneous waste

ABSTRACT

A process is provided for recycling heterogeneous waste including the initial step of subjecting the heterogeneous waste to pyrolysis to produce a synthesis gas stream comprising at least carbon monoxide and hydrogen and a molten pyrolysis product stream having a variable composition comprising at least a mineral material and a metallic material. The molten pyrolysis product stream is converted to a plurality of commercial grade solid materials. Likewise, the synthesis gas stream is also converted into at least one commercial grade chemical.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates generally to a process for recycling mixed wasteand more particularly to a process for maximizing the recycling of aheterogeneous hazardous waste stream having an uncontrolled, fluctuatingcontent of carbon, metal, and minerals into separate, non-hazardousrecycled components.

2. Description of Related Art

There is an ongoing need to dispose of hazardous waste generated byindustries, most particularly the chemical industry. Hazardous waste isoften either buried or burned, either of which can be costly processes,significantly increasing production costs for the products produced bythe relevant industry. The costs for the disposal of hazardous wastetypically, in part reflect the excise taxes and fees which must be paidto legally dispose of the waste. However, such hazardous waste disposalexcise taxes and fees may be reduced or avoided totally by recycling thehazardous waste into commercial grade chemicals and materials, therebydecreasing the overall costs associated with disposal of the waste.

Gasification is one method of disposing of hazardous waste materials.Typically, the gasification process involves the step of “pyrolysis”,which involves heating the waste material to a temperature wherein anywater, hydrocarbons, and organic compounds are volatilized and theremaining mineral and metallic constituents are melted into a moltenslag. After cooling and solidifying, the molten slag may either bedisposed of or utilized in the production of steel. The volatilizedhydrocarbons and organic compounds are generally disposed of by burning,and may in fact be consumed as an energy source. However, under currentregulations, energy recovery of this sort from hazardous waste is stillclassified as disposal rather than recycling, thereby still incurringthe full amount of taxes and fees associated with disposing of hazardouswaste.

However, rather than burning the hydrocarbons and organic compounds, ifthe oxygen concentration present during the gasification process iscontrolled, it is possible to partially oxidize the vaporizedhydrocarbons and organic compounds producing a “synthesis gas” which maybe further processed. Synthesis gas typically includes substantialquantities of hydrogen (H₂) and carbon monoxide (CO), accompanied bylesser quantities of carbon dioxide (CO₂) and water (H₂O). Synthesis gasis a raw material suitable for the production of a number of commercialgrade chemicals such as, for example and not limitation, ammonia,methanol, and dimethyl ether. Since the use of a synthesis gas togenerate commercial products is classified as recycling under currentregulations, the excise taxes and fees associated with hazardous wastedisposal can be avoided by recycling the synthesis gas in this manner.

Methanol and dimethyl ether are both typically produced from synthesisgas on an industrial scale by a process involving the catalyticconversion of carbon monoxide and hydrogen. Methanol is produced fromsynthesis gas in the presence of a methanol synthesis catalyst by thereaction (2H₂+CO→CH₃OH). Dimethyl ether is produced by the dehydrationof methanol in the presence of a methanol dehydration catalyst by thereaction (2CH₃OH→H₂O+CH₃OCH₃). Accordingly, it is often desirable toco-synthesize methanol and dimethyl ether in a reactor containing both amethanol synthesis catalyst and a methanol dehydration catalyst.

Conventional methods of forming methanol require careful balancing ofthe ratio of H₂ to CO present in the synthesis gas during the catalyticsynthesis of methanol to approximately 2:1. An excess of carbon monoxidein the synthesis gas will result undesirable levels of carbon dioxideand carbon in the reactor, creating an exothermic event that overheatsand ruins the catalyst. Conversely, an excess of hydrogen producesundesirable amounts of waste water during the methanol synthesisreaction which results in economically unfeasible treatment andpurification costs. Accordingly, careful control of the composition andflow rate of the feedstock used to produce the synthesis gas isnecessary for production of methanol or methanol and dimethyl ether.

For example, in one conventional process, coal is gasified using astrictly controlled feed rate of oxygen, in order to obtain a synthesisgas having a uniform composition and at a uniform rate. In anotherconventional process, methane is converted into a synthesis gas in areaction with a precisely controlled amount of steam to produce asynthesis gas having a uniform composition at a uniform rate. In each ofthese cases, the feed material from which the synthesis gas is producedhas a uniform composition, thereby allowing narrow control of the ratioof H₂ to CO in the synthesis gas.

Unfortunately, most industrial and hazardous wastes do not contain auniform mixture of materials. Workers commonly throw a variety ofundesirable items into the waste receptacles. Additionally, hazardouswaste can contaminate the containers within which it is stored andtransported, creating additional waste. Accordingly, the use ofheterogeneous industrial and hazardous waste in a conventionalgasification processes will result in a synthesis gas having a widelyvarying ratio of H₂ to CO. Thus, it has generally been thought that suchheterogeneous industrial and hazardous wastes are unsuitable for use inthe production of a synthesis gas suitable for the production ofmethanol and dimethyl ether.

Accordingly, it is an object of the present invention to provide aprocess for maximizing the recycling of heterogeneous waste, such asmunicipal solid waste, industrial waste and hazardous chemical wasteinto a plurality of commercial grade products and chemical compounds,thereby realizing economic gains from the resale of the commercial gradeproducts avoiding excise taxes and fees associated with disposal of thewaste.

Furthermore, it is an object of the present invention to provide aprocess for converting heterogeneous waste comprising a large number ofmiscellaneous, unidentified substances into a plurality of productstreams having known compositions.

It is yet another object of the present invention to provide a systemfor converting heterogeneous carbon-containing waste into a synthesisgas having a desired composition suitable for the synthesis of methanoland/or dimethyl ether.

SUMMARY OF THE INVENTION

The above objectives are accomplished according to the present inventionby providing a process for recycling heterogeneous waste including theinitial step of subjecting the heterogeneous waste to pyrolysis toproduce a synthesis gas stream comprising at least carbon monoxide andhydrogen and to produce a molten pyrolysis product stream having avariable composition comprising at least a mineral material and ametallic material. The molten pyrolysis product stream is converted to aplurality of commercial grade solid materials. Likewise, the synthesisgas stream is also converted into at least one commercial gradechemical.

BRIEF DESCRIPTION OF THE DRAWINGS

The construction and design to carry out the invention will hereinafterbe described together with other features thereof. The invention will bemore readily understood from a reading of the following specificationand by reference to the accompanying drawings forming a part thereof,wherein an example of the invention is shown and wherein:

FIG. 1 is a block diagram illustrating the basic material flow pathwaysby which heterogeneous waste is recycled in accordance with a preferredembodiment of the present invention.

FIG. 2 is a schematic illustrating the basic operation of a gasifier foruse in accordance with a preferred embodiment of the present invention.

FIG. 3 is a block diagram illustrating a methanol purification processin accordance with a preferred embodiment of the present invention.

FIG. 4 is a block diagram illustrating a methanol and dimethyl etherpurification process in accordance with a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now in more detail to the drawings, the invention will now bedescribed in detail. As shown in FIG. 1, a heterogeneous waste recyclingprocess A converts a heterogeneous mixture of waste material into aplurality of commercially useful solid products and chemical compounds.The term “heterogeneous waste material” as used herein refers to anon-homogeneous carbon-containing feedstock, the composition of whichcan vary widely over time as the result of variations in the compositionof one or more of the feedstock components and/or variations in therelative amounts of the components in the feedstock. Solid and liquidcarbon-containing waste materials containing large amounts of inorganicmaterial are processable as heterogeneous feedstock according to thepresent invention. The carbon content of heterogeneous waste material AAwill generally vary by more than ten weight percent over a giventwenty-four hour period. However, in its preferred embodiment, theprocess of the present invention is capable of processing heterogeneouswaste material AA having a carbon content varying by as much as thirtyweight percent to fifty weight percent over a twenty-four hour period.Preferably, the net heating value of the heterogeneous feedstock isgreater than approximately three thousand Btu/lb. Examples of thecarbon-containing waste material that can be processed according to thepresent invention include municipal solid waste and hazardous industrialwastes such as oil-contaminated dirt, demolition debris, respiratormasks, paint and contaminated rags.

As shown in FIG. 1, heterogeneous waste material AA is compressed in awaste compaction press 12 and fed into a gasifier 14 wherein it ispyrolytically converted into an undifferentiated molten slag stream BBand a raw synthesis gas stream CC having a variable ratio of H₂ to COunsuitable for conversion to methanol by conventional methods.Undifferentiated molten slag stream BB is allowed to gravitationallyseparate to produce a molten mineral stream DD and a molten ferric alloystream EE which are water quenched in a quenching chamber 16. Oncequenched, molten mineral stream DD yields a vitreous material suitablefor commercial use as an industrial abrasive and molten ferric alloystream EE yields a ferric alloy suitable for commercial use in diecasting metal production processes or as a shock blast material. Thevitreous material and ferric allow material are magnetically separatedby magnetic separator 17.

With respect to raw synthesis gas stream CC, the H₂:CO ratio is adjustedto render it suitable for the production of methanol or methanol anddimethyl ether. First, the H₂:CO ratio of raw H₂ synthesis gas stream CCis detected by synthesis gas composition sensor 18 and, in response tothe sensed value thereof, a first portion FF of raw synthesis gas streamCC is directed via operation of a shift bypass valve 68 to shift reactor22 while the remaining portion GG of raw synthesis gas stream CC flowsthrough a shift reactor bypass line 24. Within shift reactor 22, firstportion FF of raw synthesis gas stream CC is reacted with a selectedamount of steam HH, both converting the CO therein to CO₂ and producingadditional H₂ via the shift reaction (CO+H₂O→CO₂+H₂) to produce ashifted gas stream II predominantly comprising CO₂ and H₂. Shifted gasstream II is then mixed with remaining portion GG of raw synthesis gasstream CC to form a mixed synthesis gas stream JJ having a desired ratioof H₂ to CO and including substantial quantities of CO₂. Mixed synthesisgas stream JJ is directed to a CO₂ removal unit 26 wherein approximatelygreater than 98% of its CO₂ content is removed, producing a CO₂ depletedmixed synthesis gas stream KK and a CO₂ stream LL suitable forpurification into commercial grade CO₂. CO₂ depleted mixed synthesis gasstream KK is then converted in a liquid phase catalyst reactor 28 to auseful product stream MM comprising methanol or a combination ofmethanol and dimethyl ether and subjected to separation and purificationby methanol/DME recovery unit 30.

Alternatively, raw synthesis gas stream CC may also be utilized for thesynthesis of ammonia according to the process disclosed in U.S. patentapplication Ser. No. 09/200,150, entitled “Process for making Ammoniafrom Heterogeneous Feedstock,” which is hereby incorporated by referencein its entirety. For conversion to ammonia, all of raw synthesis gasstream CC is directed through a shift reactor wherein its CO content iscompletely converted to CO₂ . Subsequently, the CO₂ is removed and theresulting stream of purified hydrogen is reacted with nitrogen toproduce commercially useful ammonia.

As illustrated in FIG. 2, according to the process of the presentinvention, a quantity of a heterogeneous waste material AA is firstcompacted by a waste compaction press 12 mounted at the front of agasifier 14 into plugs having approximately similar dimensions and mass.In addition to forming plugs of heterogeneous waste material AA, wastecompaction press 12 also operates to force the compacted plugs ofheterogeneous waste material AA into gasifier 14. In the preferredembodiment, waste compaction press 12 includes a conventional steelpress rated at a maximum capacity of 320 psi, although any conventionalpress having sufficient capacity will suffice. Each compression cycle ofwaste compaction press 12 results in the introduction of a similarlysized plug of heterogeneous waste material into gasifier 14.Accordingly, the feed rate of heterogeneous waste material into gasifier14 may be regulated simply by altering the cycle time of wastecompaction press 12. In the preferred embodiment, waste compaction press12 operates at a rate on the order of approximately 20 cycles per hour.

Gasifier 14 may be any conventional gasifier. Preferably, gasifier 14 isof the type disclosed in U.S. Pat. Nos. 5,788,723, 5,711,924, 5,282,431and 5,707,230, which are incorporated herein by reference in theirentireties. In the preferred embodiment, gasifier 14 includes anexternally heated gasifier vessel 40 having a feed aperture 42 locatedalong its midplane, a synthesis gas outlet 44 located at its upper endand a slag outlet 46 located at its bottom end. Feed aperture 42 servesas an open conduit to the atmosphere through which compacted plugs ofheterogeneous waste material AA may be fed by press 12 into gasifiervessel 40. Accordingly, gasifier 14 operates at approximatelyatmospheric pressure. Upon injection into gasifier vessel 40,heterogeneous waste material AA is subjected to gasification by beingheated to a pyrolysis temperature generally between 2000° C. and 3000°C., sufficient to volatilize any water, hydrocarbons, and other organiccompounds entrained therein. The mixture of volatilized gases rises tothe top of gasifier vessel 40 where it may undergo further reactionprior to exiting gasifier vessel 40 through synthesis gas outlet 44.

Meanwhile, the solid portions of heterogeneous waste material AA,including non-volatile organic compounds, metals, minerals and metallicoxides, fall to the bottom of gasifier vessel 40 forming a gasifier feedpile NN which is eventually melted into an undifferentiated molten slagstream BB. A selected amount of oxygen is injected into the lowerportion of the gasifier vessel 40 to react with carbon and non-volatileorganic compounds in gasifier feed pile CC, liberating additional CO,CO₂ and H₂O into the gasifier vessel headspace. The remainder ofundifferentiated molten slag stream BB flows through slag outlet 46 toan elongated separation chamber 54.

An excess carbon inventory should be maintained within the interior ofgasifier vessel 40 in order to prevent an exothermic reaction of oxygenwith the carbon monoxide in the pyrolysis gas, which can result indamage to gasifier vessel 40 and potentially an explosive exothermicevent. In the preferred embodiment, this carbon excess is ensured bymonitoring the height of gasifier feed pile NN and adjusting feed rateof heterogeneous waste material AA to maintain gasifier feed pile NNabove a minimum height which assures that an excess carbon inventory ispresent within oxygen to gasifier vessel 40. The height of gasifier feedpile NN is preferably sensed by a gamma ray attenuation detector 50,which measures the attenuation of gamma radiation emitted from a source52 having a known intensity diminution as it passes through gasifierfeed pile NN.

In the preferred embodiment, undifferentiated molten slag stream BBflows through slag outlet 46 to separation chamber 54 wherein thecomponents of the slag gravitationally separate into a layer of mineralmaterial floating on top of a layer of molten ferric alloy. Separationchamber 54 includes weir 56 over which the upper mineral layer and lowerferric alloy layer alternatively flow. The molten mineral stream andmolten ferric alloy stream are then quenched in a quenching chamber 16,which includes a 30 inch diameter tube through which the molten materialfalls while being sprayed with jets of water which breakup the moltenmaterial into small particles while quenching it. The quenched particlesthen fall to the bottom of quenching chamber 16.

Upon quenching. the molten mineral stream DD, solidifies into particlesof a vitreous material having a specific gravity of approximately 2.25.The vitreous material is generally useful as an airblast abrasive whenpulverized to an appropriate size. This is a particularly usefulcommercial product since a market exists for approximately one milliontons of such airblast abrasive per year and the current primary sourcesfor this material, coal fired power plants, are currently being phasedout. Upon quenching the molten ferric alloy stream EE, solidifies intoparticles of a steel shot, wherein the majority of environmental metalsare alloyed into the steel. This steel shot is generally suitable foruse as feedstock into die casting metal production processes or, aftertempering, as a shock blast material.

Following quenching, the mixed particles of vitreous material and steelshot are transferred by a bucket elevator from the bottom of quenchingchamber 16 to a magnetic separator 17. Magnetic separator 17 operates toseparate the particles into a steel shot product stream comprisingparticles of the ferrous alloy and a vitreous stream comprisingparticles of the vitreous material.

The temperature of the pyrolysis gas in gasifier vessel 40 is preferablymaintained at a value of at least 2100 degrees C., sufficient to crackentrained hydrocarbons to form a carbon soot and H₂ and to drive theendothermic reactions necessary for the production of a synthesis gasrich in H₂ and CO. Steam produced by the heat of fusion liberated by thequench reactions of the mineral and ferric slag streams flows as acounter current back into the gasifier vessel 40 allowing for theconversion of carbon from soot and entrained hydrocarbons to CO in thepyrolysis gas via the endothermic reaction (C+H₂O→CO+H₂), furtherincreasing the concentrations of CO and H₂ in the synthesis gas.Additionally, a substantial amount of the carbon and CO₂ in thepyrolysis gas is also converted to CO via the Boudard reaction(CO₂+C→2CO).

The temperature and gas flow rate of gasifier vessel 40 are controllableto desired values as follows. The temperature of the pyrolysis gas inthe upper portion of gasifier vessel 40 is controllable by adjusting therate at which oxygen is injected into the upper portion of gasifiervessel 40 to exothermically react with carbon, CO and H₂ therein.Accordingly, temperature of the pyrolysis gas is increased by increasingthe amount of oxygen injected into the upper portion of gasifier vessel40 and decreased by decreasing amount of oxygen injected into the upperportion of gasifier vessel 40. In the preferred embodiment, a smallamount of methane may also be injected with the oxygen into the upperportion of gasifier vessel 40 to avoid quenching the pyrolysis gas priorto injection of the oxygen.

The flow rate of gas exiting gasifier vessel 40 is controllable byaltering the rate at which oxygen is injected into the bottom portion ofgasifier vessel 40. To increase the flow rate of gas leaving gasifiervessel 14, the flow rate of oxygen into the bottom portion of gasifiervessel 40 is increased, driving the exothermic gasification of carbonand non-volatile organic constituents of gasifier feed pile NN into CO,H₂ and CO₂, thereby increasing the gas flow rate leaving gasifier vessel40. Increasing the flow of oxygen into the bottom portion of gasifiervessel 40 may also necessitate increasing the feed rate of heterogeneouswaste material AA into gasifier vessel 40 to compensate for theadditional consumption of material from gasifier feed pile NN. Ofcourse, increasing the feed rate of heterogeneous waste material AA intogasifier vessel 40 will increase the amount of steam flowing back intogasifier vessel from quenching the resulting increased flows of moltenmineral material DD and molten ferric alloy EE, which may also serve toincrease the gas flow rate since the steam may react with carboncomponents in gasifier feed pile NN to produce CO, H₂ and CO₂.Conversely, to reduce the gas flow rate exiting gasifier vessel 40, theoxygen injection rate into the bottom portion of gasifier vessel 40 issimply decreased.

The raw synthesis gas CC exiting gasifier vessel 40 through synthesisgas outlet 44 has a variable composition, typically comprising at leastcarbon monoxide (CO), carbon dioxide (CO₂) and hydrogen (H₂). The rawsynthesis gas CC preferably has a composition of approximately twentyvolume percent to approximately fifty-four volume percent of both CO andH₂, with the amount of CO exceeding the amount of H₂. Additionally, rawsynthesis gas CC will usually include approximately twenty volumepercent to thirty volume percent CO₂. The raw synthesis gas CC exitinggasifier vessel 40 also may include approximately 1% carbon soot andtrace amounts of sulfur, halogens, and volatile metals.

Next, the raw synthesis gas CC is directed to gas treatment system 58wherein it is quenched with water at a 25:1 water/gas ratio. The quenchreaction occurs through a complex reversing flow which shock cools rawsynthesis gas stream CC to approximately 156° F. The use of high speedshock cooling ensures that there is no time for the de novo synthesis ofdioxins and dibenzofurans during the quench. In addition to cooling rawsynthesis gas stream CC, the quench water serves to remove the majorityof contaminating soot from raw synthesis gas stream CC. The quench wateralso absorbs halogens and the majority of contaminating sulfur. Thislowers the pH of the quench water to approximately two, increasing thequench water's solubility for metals and thereby allowing it to alsodissolve the majority of contaminating metals from raw synthesis gasstream CC. In the preferred embodiment, the quench water is subjected toa series of conventional water filtration and precipitation treatmentsteps, as would be known to one of ordinary skill in the art, whereinthe majority of these contaminants are separated and recycled.

Following the water quench, raw synthesis gas stream CC preferablyundergoes a series of wash steps to further remove contaminants. First,raw synthesis gas stream CC is subjected to an alkaline wash to removeany acid radicals. Next, raw synthesis gas stream CC is subjected to aglycerin wash to remove hydrophobic carbon particles. Next, rawsynthesis gas stream CC is subjected to a sulfur chealating wash, usinga sulfur chealating agent which removes H₂S, COS and other contaminatingsulfur compounds. Next, raw synthesis gas stream CC is subjected to achilled water wash at approximately 45° F. to condense mercury. Finally,raw synthesis gas stream CC is reheated to approximately 113° F. andpassed through an activated carbon filter for a final polish. In thispresently preferred system, following the wash steps, raw synthesis gasstream CC is extremely pure, having approximately 50 parts per billionsulfur, 50 parts per billion halogens and 10 parts per billion of heavymetals.

As previously mentioned, the stoichiometric ratio of H₂ to CO requiredfor the synthesis of methanol is 2:1. Conventional processes formethanol synthesis are run in a reactor at an excess of H₂, for examplehaving H₂:CO ratios of 2.1-2.2:1, in order to avoid overheating thecatalyst or sooting up the catalyst through the deposition of carbonupon the methanol synthesis catalyst. Unfortunately, the excess hydrogenin the process results in the production of greater amounts of wastewater from the reaction. As this waste water contains detectablepercentages of methanol and other byproducts, it must be treated priorto release. Therefore, minimization of the amount of waste waterproduced during the reaction would be desirable.

In the present process, therefore, the synthesis gas fed into themethanol synthesis reaction is desired to have at most no more than thestoichiometric amount of hydrogen, and preferably less than thestoichiometric amount of hydrogen, thereby minimizing the generation ofwaste water. For example, in the preferred embodiment, the ratio ofH₂:CO of the synthesis gas fed to the reactor should preferably be COrich, between 1.95-2.0:1 inclusive, for the synthesis of methanol.Accordingly, it is necessary to adjust the ratio of H₂:CO of thesynthesis gas to the desired range.

As shown in FIG. 1, after washing, the ratio of H₂:CO in raw synthesisgas stream CC is sensed by a raw synthesis gas composition sensor 18. Inthe preferred embodiment, raw synthesis gas composition sensor 18includes an infrared spectrophotometric sensor 62 for sensing theamounts of CO and CO₂ in raw synthesis gas stream CC and a specific heatsensor 64 for sensing the amount of H₂ in raw synthesis gas stream CC.Infrared spectrophotometric sensor 62 operates generally by measuringthe absorption, at wavelengths specific for CO and CO₂ respectively, ofa beam of infrared light passing through raw synthesis gas CC. Specificheat sensor 64 is an online gas analyzer which operates by diverting asample flow from raw synthesis gas stream CC, heating the sample streamto a known temperature, and then adding a standard energy input, such asfrom a heating filament, and measuring the change in temperature of thesample stream to determine the specific heat of raw synthesis gas streamCC. Since the specific heat of H₂ is approximately an order of magnitudehigher than the specific heats of CO and CO₂ respectively, the specificheat of raw synthesis gas stream CC directly relates to its approximatehydrogen content.

Raw synthesis gas stream CC is compressed to a pressure of, for example,about 160 psi or more, using raw synthesis gas compressor 60 in order todrive it through subsequent process steps. The ratio of H₂:CO of the rawsynthesis gas CC is adjusted by directing a first portion FF of rawsynthesis gas stream CC into a shift reactor 22, while the remainingportion GG of raw synthesis gas stream CC flows through a shift reactorbypass line 24. The percentage of raw synthesis gas stream CC divertedinto shift reactor 22 is controlled by regulating the position of shiftbypass valve 68 in response to the sensed composition of raw synthesisgas stream CC. In the preferred embodiment, the percentage of rawsynthesis gas stream CC to be diverted is controlled in response to themeasured ratio of H₂:CO of raw synthesis gas stream CC.

Within shift reactor 22, a selected amount of water HH, in the form ofsteam, is mixed with first portion FF of raw synthesis gas stream CC.The steam and CO in the first portion FF of raw synthesis gas stream CCreact via the shift reaction (CO+H₂O→CO₂+H₂) to produce a shifted gasstream II containing primarily CO₂ and H₂. In the preferred embodiment,substantially all (approximately ninety eight percent) of the CO contentof first portion FF of raw synthesis gas stream CC is converted intoCO₂. The amount of steam injected into shift reactor 22 is selected toapproximately correspond to the CO content of first portion FF of rawsynthesis gas stream CC based upon the sensed H₂:CO ratio of rawsynthesis gas stream CC, thereby maximizing conversion of CO to CO₂ andminimizing the water content of shifted gas stream II.

In a simplified exemplary embodiment, the percentage of raw synthesisgas stream CC which must be diverted into shift reactor 22 is generallydetermined under the relationship x=(2y-z)/3y, wherein x is the percentof raw synthesis gas stream CC to be shifted, y is the initialpercentage of raw synthesis gas stream CC which is CO and z is theinitial percentage of raw synthesis gas stream CC which is H₂. Thisrelationship takes into account both the decrease in CO and the increasein H₂ which result from the shift reaction. For example, to shift a rawsynthesis gas stream CC having a composition of 40 percent CO, 30percent H₂, and 30 percent CO₂ to a desired H₂:CO ratio of 2:1 we findthat x=(2(0.4)-0.3)/3(0.4) which simplifies to x=0.4166 or 41.66%.Therefore, to shift a raw synthesis gas stream CC having a compositionof 40 percent CO, 30 percent H₂, and 30 percent CO₂ to a desired H₂:COratio of 2:1, approximately 41.66% of the flow of raw synthesis gasstream CC must be directed to shift reactor 22.

Shifted gas stream II is then mixed with remaining portion GG of rawsynthesis gas stream CC to form a mixed synthesis gas stream JJ havingthe approximate desired H₂:CO ratio (approximately 1.95 to 2.0) andincluding substantial quantities of CO₂. The actual ratio of H₂:CO inmixed synthesis gas stream JJ is sensed by mixed synthesis gascomposition sensor 70 and may be used as a trim signal to make minoradjustments to the bypass flow rate and steam flow rate to shift reactor22. Mixed synthesis gas composition sensor 70 may be any means ofsensing the composition a raw synthesis gas stream CC which would beknown to one of ordinary skill in the art. However, in the preferredembodiment, mixed synthesis gas composition sensor 70 includes aninfrared spectrophotometric sensor 72 and a specific heat sensor 74similar to those of raw synthesis gas composition sensor 18.

In the preferred embodiment, mixed synthesis gas stream JJ issubsequently directed to a CO₂ removal unit 26 wherein approximatelygreater than 98% of its CO₂ content is removed, producing a CO₂ depletedmixed synthesis gas stream KK having the desired ratio of H₂:CO and aCO₂ stream LL suitable for purification into commercial grade CO₂. Inthe preferred embodiment, CO₂ removal unit 26 operates by passing mixedsynthesis gas stream JJ through an aqueous solution of an amine basewhich capable of binding the carbonic acid form of CO₂. Of course, oneof ordinary skill in the art will recognize that CO₂ removal unit 26 maybe selected from a number of other conventional CO₂ removal systems.Also, in alternative embodiments, the carbon dioxide from the shiftreaction can be left in the synthesis gas and removed following theformation of the methanol and/or dimethyl ether, if desired, withoutadversely affecting the reaction except by increasing the amount ofwaste water in the product.

The CO₂ depleted mixed synthesis gas stream KK is next preferablycompressed to approximately 950 psia by mixed synthesis gas compressor78 and directed into liquid phase catalyst reactor 28 for conversioninto a useful product stream MM comprising either methanol or a mixtureof methanol and dimethyl ether. Liquid phase catalyst reactor 28 ispreferably of the type developed by Air Products and Chemicals, Inc., asdisclosed in U.S. Pat. Nos. 5,179,129, 5,218,003, 4,910,227, 4,766,154,5,284,878 and 4,628,066 which are incorporated herein in theirentireties by reference. As described in these references, the liquidphase reactor may be selectively operated at from approximately 750 to1500 psia to produce a product stream MM comprising either methanol or amixture of methanol and dimethyl ether from a CO rich synthesis gasstream such as CO₂ depleted mixed synthesis gas stream KK. Methanol isproduced from synthesis gas in the presence of a methanol synthesiscatalyst by the reaction (2H₂+CO→CH₃OH). Dimethyl ether is produced bythe dehydration of methanol in the presence of a methanol dehydrationcatalyst by the reaction (2CH₃OH→H₂O+CH₃OCH₃)

In the preferred embodiment, liquid phase catalyst reactor 28 operatesat a temperature of about 200° C. to 250° C. and a pressure of about 950psia. Liquid phase catalyst reactor 28 includes at least one methanolsynthesis catalyst, such as a conventional copper-containing catalyst,suspended in an inert liquid. The liquid for the liquid phase reactormay be any suitable liquid described in the foregoing referencesincorporated herein by reference, including, for example, hydrocarbons,alcohols, ethers, polyethers, etc. For producing both methanol anddimethyl ether, the liquid phase reactor should contain not only themethanol synthesis catalyst, but should also contain a methanoldehydration catalyst. The methanol dehydration catalyst can be anyconventional catalyst known in the art for this purpose including, forexample, alumina, silica-alumina, zeolites, solid acids such as boricacid, solid acid ion exchange resins such as perfluorinated sulfonicacid, etc.

Since the CO₂ depleted mixed synthesis gas stream KK has a H₂:CO ratioslightly lower than the stoichiometric value of 2.0 for the methanolsynthesis reaction, the production of waste water in liquid phasecatalyst reactor 28 is minimized. In fact, compared to conventional gasphase methanol synthesis processes that operate on the hydrogen richside of the stoichiometric value, the amount of waste water produced inthe present process is reduced on the order of ten times or more.

Liquid phase catalyst reactor 28 is effective to convert approximately40% of the CO and H₂ in CO₂ depleted mixed synthesis gas stream KK tomethanol per pass through liquid phase catalyst reactor 28. Accordingly,product stream MM also includes the remaining unreacted 60% of theinitial CO and H₂ from CO₂ depleted mixed synthesis gas stream KK.Therefore, product stream MM is next directed to condenser 80 whereinthe products methanol and dimethyl ether and any contaminating water andCO₂ are condensed to form a liquid product stream OO. The remainder ofproduct stream MM, comprising mostly CO and H₂ is then recycled backinto liquid phase catalyst reactor 28 for subsequent reaction intomethanol or methanol and dimethyl ether. By continually recycling CO andH₂ from product stream MM, near complete conversion of the CO and H₂ tomethanol or methanol and dimethyl ether may be achieved. However, smallwaste gas stream PP comprising approximately two percent of the flow ofproduct stream MM is removed from liquid phase catalyst reactor 28 via apurge line to prevent the buildup of any contaminating non-reactivegases therein.

Liquid product stream OO is fed to methanol/DME recovery unit 30 toseparate the methanol and dimethyl ether products from carbon dioxideand water. As seen in FIG. 3, when liquid phase catalyst reactor 28 isoperating in methanol only mode, methanol/DME recovery unit 30 includesa first distillation column 86 through which liquid product stream OO ispassed for separating out any carbon dioxide which may be dissolvedtherein. Liquid product stream OO then passes through a seconddistillation column 88 which separates out any contaminating water,producing a high purity methanol stream RR.

As seen in FIG. 4, when liquid phase catalyst reactor 28 is operating inmethanol/dimethyl ether mode, methanol/DME recovery unit 30 includes afirst distillation column 90 through which liquid product stream OO ispassed to separate it into a methanol/water stream SS and a dimethylether/carbon dioxide stream TT. Methanol/water stream SS is then passedthrough a second distillation column 92 which separates out anycontaminating water to produce high purity methanol stream RR. Dimethylether/carbon dioxide stream TT is passed through a third distillationcolumn 94 which separates out any contaminating carbon dioxide toproduce high purity dimethyl ether stream UU.

Thus, it may be seen, that an advantageous process to maximize therecycling of heterogeneous waste is provided according to the presentinvention. The recycling of heterogeneous waste may be maximized bypyrolytically converting it into a plurality of useful solid componentsand a synthesis gas having a variable composition, including CO and H₂.By removing a portion of CO from the synthesis gas, the composition ofthe synthesis gas may be adjusted to render it suitable for theproduction of methanol and/or dimethyl ether. Furthermore, by using aliquid catalyst reactor, the production of methanol and/or dimethylether may be accomplished while minimizing the generation of wastewater. Accordingly, by utilizing the present invention, a heterogeneouswaste material having a variable and unknown composition is convertibleinto a plurality of useful material streams having known compositions,including a ferric alloy stream, a vitreous material stream, a methanolstream, a dimethyl ether stream, a carbon dioxide stream, andmiscellaneous streams containing sulfur and salts, thereby realizingeconomic gains from the resale of the commercial grade products inaddition to receiving excise tax and fee benefits.

It thus will be appreciated that the objects of this invention have beenfully and effectively accomplished. It will be realized, however, thatthe foregoing preferred specific embodiment has been shown and describedfor the purpose of this invention and is subject to change withoutdeparture from such principles. Therefore, this invention includes allmodifications encompassed within the spirit and scope of the followingclaims.

What is claimed is:
 1. A process for recycling heterogeneous wastecomprising the steps of: subjecting the heterogeneous waste to pyrolysisto produce a synthesis gas stream comprising carbon monoxide andhydrogen and a molten pyrolysis product stream comprising at least amineral material and a metallic material; converting said moltenpyrolysis product stream to a plurality of useful solid materials by:allowing said molten pyrolysis product stream to gravitationallysegregate into metallic portion and a mineral portion; quenching saidmetallic portion of said molten pyrolysis product stream to form aferric alloy; quenching said mineral portion of said molten pyrolysisproduct stream to form a vitreous material; and converting said gaseouspyrolysis product stream into at least one useful chemical by: sensingthe ratio of hydrogen to carbon monoxide of said synthesis gas stream;in response to said sensed ratio of hydrogen to carbon monoxide of saidsynthesis gas stream, separating said synthesis gas stream into a firststream and a second stream; introducing said first stream into a shiftreactor, said shift reactor increasing the ratio of hydrogen to carbonmonoxide of said first stream to produce a shifted gas stream; mixingsaid shifted gas stream with said second stream to produce a mixedsynthesis gas stream, said mixed synthesis gas stream having a desiredratio of hydrogen to carbon monoxide; and converting said mixedsynthesis gas to at least one commercial grade chemical selected fromthe group consisting of ammonia, methanol or dimethyl ether.
 2. Theprocess of claim 1 wherein said desired ratio of hydrogen to carbonmonoxide is in the range of approximately 1.95 to approximately 2.0molecules of hydrogen per molecule of carbon monoxide.
 3. The process ofclaim 1, wherein said heterogeneous waste has a net heating value of atleast 3000 BTU/lb.
 4. The process of claim 1, wherein said pyrolysisstep is conducted in a gasifier and wherein an excess carbon inventoryis maintained in said gasifer during said pyrolysis step.
 5. The processof claim 1, wherein said commercial grade chemical is produced byreacting said synthesis stream with a catalyst in a liquid phasereactor.
 6. The process of claim 1, wherein said commercial gradechemical is methanol and said methanol is produced in a liquid phasereactor including a methanol synthesis catalyst.
 7. The process of claim1, wherein said commercial grade chemical is dimethyl ether and saiddimethyl ether is produced in a liquid phase reactor including amethanol synthesis catalyst and a methanol dehydration catalyst.
 8. Theprocess of claim 1, further including the step of recovering thecommercial grade chemical.
 9. The process of claim 8, wherein saidrecovering step includes the step of recovering the commercial gradechemical from a distillation column which separates the commercial gradechemical from water.
 10. The process of claim 9, further including thestep of condensing said commercial grade chemical from the gas exitingsaid liquid phase reactor and wherein unreacted synthesis gas componentsare recycled back to said liquid phase reactor.
 11. The process of claim1, wherein said mixed synthesis gas stream further includes carbondioxide and said process further includes the removal a portion of saidcarbon dioxide from said synthesis gas stream.